Process for preparing biliary acids having a ketonic function



. Patented June 3, 1941 PROCESS FOR PREPARING BILIARY ACIDS HAVING KETONIC FUNCTION Raymond Charonnat, Ivry sur Seine, and Alain Horeau, Paris, France, assignors to Chimie et Atomistique, Paris, France, a French company No Drawing. Application January 20, 1939, Serial No. 251,918. In France February 1, 1938 18 claims. (01160-39711) It is a known fact that the biliary acids having a 'ketonic function (dehydrocholic acid, dehydrodesoxychloic. acids, dehydrolithocholic acids, etc.) are prepared by the oxidation of hydroxylated biliary acids, the natural constituents of the bile of animals; among the principal of these are cholic or cholalic acid, the desoxycholic acids (chenodesoxylic acid, hyodesoxycholic acid, etc.)

the lithocholic acids, etc.

Hitherto, the principal oxidizing agent employed was chromic acid, or the alkaline chrmates, which can only be used when the acids to be oxidized are in solution. However, as the hydroxylated biliary acids are insoluble in water, the necessary preliminary solubilization usually takes place in glacial acetic acid. This process is expensive, as it is necessary to employ a great excess of acetic acid in order to maintain the biliary acid in solution, and it is particularly difficult to recover the solvent in this case.

It has been proposed to efi'ect the chromic oxidation, in an aqueous solution, by precipitating the biliary acid in an indifferent liquid which is 7 not miscible with water, or otherwise on an inert substance, in order to distribute the acid to be oxidized upon a large surface for facilitating the action, but while the reaction must be carried out at a temperature near 3040 0., which requires a heating or cooling, the final separation, in the pure state, of the oxidation product is troublesome.

A. known method is also employed for effecting the oxidation by means of potassium permanganate.

These two oxidizing agents, chromic acid and permanganate. have the disadvantage of causing an oxidation which it is difiicult to keep under control, as it may take place in an incomplete manner, or on the contrary, if an excess of the oxidizing agent is employed, or if the temperature is allowed to rise, products of a more advanced oxidation will be formed, such as the bilianic or cilianic acids for example.

In both of these cases, the industrial yield from the operation is defective, and it is necessary to separate the useful acid which is formed. from the by-products which are not oxidized or are oxidized to excess. This purification is expensive, it still further decreases the yield, and is diflicult to carry out completely in order to obtain a pure product. In fact, it is observed that the specimens of dehydrocholic acid, for instance, which are placed on the market, have in all cases a melting point (229-234 C.) which is lower by a few degrees than the melting point (240 C.) of the pure acid.

Moreover, the said oxidizing agents have a considerable tinctorial power, and the resulting products are never perfectly white, and thus their market value is reduced.

In order to obviate these various drawbacks, it was necessary:

1) To find an oxidizing agent which acts quantitatively, in the cold state, in a medium which is simply aqueous and can be readily discoloured without risk of alteration of the finished product which may retain traces of the same;

(2) To determine the conditions of use of this oxidizing agent in order that the oxidation, after it has commenced, will stop by itself, automatically, at the product to be prepared.

The present invention relates to a process for the preparation of biliary acids having a ketonic function which complies with these conditions and which is based upon the following general principles:

(1) The hydroxylated biliary acids are in the first place, and before any oxidation, transformed into one of their salts (of sodium or potassium, for instance) or one of their esters, which are soluble in water. The direct oindation in an aqueous medium, without the use of any other expensive solvent, can then be effected.

' (2) The oxidizing agent employed is bromine, whose action can be controlled with great accuracy. The succeeding discoloration can be readily effected by the addition of a trace of bisulphite.

(3) The oxidation takes place in a medium in which the pH is kept constant during the whole time of the operation, by the elimination of the hydrobromic acid as fast as it is formed, either by the use of a butter solution or by any other known means. A suitable value of said pH is comprised for instance between 7,5 and 8,5.

(4) The reaction takes place in the cold state.

The said process has the advantage of taking place in a concentrated aqueous solution, in a homogeneous phase, without heating or supervision of any kind; the resulting crude product is in a very pure state.

It further provides for efiecting the oxidation by stages, and for obtaining monoand diketonic derivatives from the diand trihydroxylated biliary acids. Moreover, the oxidation by the said process is efiected with sufilcient caution to permit the ketonization of the biliary acids in the presence of taurine and of glycocoll, i. e., the crud natural biliary acids, which had not cholalate, to which is added, in the cold state,

5 molecules of sodium bicarbonate, for instance (buffer solution), then pour in 6 atoms of liquid bromine.

The reaction takes place according to the following formula:

csmtronncoma+enr== CzsHas (O) :COzH-i-5BrH+BrNa Leave this for 24 hours at the ordinary temperature stirring occasionally. The bromine, which forms a mass at the bottom of the vessel, dissappears very rapidly at first, and then gradually, owing to the reaction of the sodium bicarbonate on the hydrobromic acid according as this latter is formed, carbon dioxide gas is driven off, and the dehydrocholic acid gradually precipitates in a very pure state. After 24 hours, the greater part of this latter (87% of the theoretical yield) has precipitated. The product is then centrifugated and washed with a solution of commercial bisulphite at dilution, and then with water. This affords a very white substance, whose melting point is 230, which can be purifled by recrystallization (melting point 239.5). The filtrate still contains a small amount of bromine: it will no longer precipitate, and does not become discoloured in 24 hours. Add bisulphite at dilution, drop by drop, until the bromine has disappeared. Then acidulate with dilute sulphuric acid. A fresh portion of dehydrocholic acid, almost as pure as the first one, will again precipitate, and this now affords about 9% of the theoretical yield. The total yield isthus raised to 96%.

As already mentioned, it is possible to effect the oxidation by stages and to oxidize readily and as desired in the di-, trior polyhydroxylated biliary acids only one, a plurality or all of the alcoholic functions in order to transform the same into ketonic functions.

When starting for instance from the cholic acid (3, 7, 12 trihydroxycholanic) and when oxidizing successively a first, then a second and afterwards the third alcoholic function, it is possible to obtain the dihydroxymonoketocholanic acid, the hydroxydiketocholanic acid, their isomers and the 3, 7, 12 triketocholanic acid (dehydrocholic acid).

According to the invention, one, two, three or n alcoholic functions are transformed into one, two, threeor n ketonic functions while treating one molecule of a salt of the suitable biliary acid with one, two, three or n molecules of bromine.

The oxidation is to be made with a constant pH and preferably. at a temperature of about 0 C.

Preferably also, it is possible to oxidize only one function at a time. In this case, it will be sufiicient to begin the oxidation with only one molecule of bromine; as soon as the reaction is completed, a second function is oxidized by the use of a second molecule of bromine and so on. The order in which the successive hydroxyl groups C23Hae(OH)aCOOH, having the developed formula cm on. 0

H-CHr-CH:C\ n 11 13 Q 0H noon by the minimum quantity of alkali required. This affords a solution of cholate, to which is added, at about 0 0., a few molecules of sodium bicarbonate for instance (buffer solution), and then pour in one molecule of an aqueous solution of bromine. The reaction takes place according to the following formula:

This is allowed to stand for a few hours at about 0 C. stirring occasionally. The bromine disappears very rapidly and then gradually, and the sodium salt of the dihydroxymonoketocholanic acid is formed. The product is then precipitated by an acid, centrifugated and washed with water.

This affords, after another crystallisation in aqueous alcohol, a new compound not disclosed in the chemical literature and having the following properties:

Melting point: 171' C.

[oz]D= ---4.5' in a 20% alcoholic solution.

It crystallises with two molecules of water and has for its formula CnH:s(OH) :O-COOH, 2320.

Applicants have found that one of the alcoholic functions in the positions I or 12 has been transformed by oxidation into a ketonic function, but hitherto they have been unable to decide between these two positions 7 and 12.

When the resulting monoketonic derivative is subjected to another treatment like the preceding with another molecule of bromine, this affords the hydroxydiketocholanic acid obtained from the cholic acid by the transformation to two aicoholic functions into two ketonic functions. The compound thus obtained has the following formula:

Cal-I34 (OH) Oz-COOH The new compound, not disclosed in the chemical literature, is slightly dextrorotatory, whereas the initial compound (dihydroxymonoketocholanic acid) is levorotatory; it was first dimcult to be crystallized, but it has been finally possible to obtain it as crystals melting at 129.5 C.

Moreover, when the hydroxydiketocholanic acid is treated in the same conditions as aforesaid, it

The flitrates can be treated as above indicated a in order to provide for the recovery of useful byproducts. I

It is possible. to modify the natural order in which the diilerent alcoholic functions are oxidized, by substituting one and/or another of said functions by a compound such as an ester, an ether or another compound, which prevents said function or functions from beingtoxidized in the conditions provided by the invention. When the alcoholic functions remaining unaltered will then have been oxidized by bromine, it will be sufficient to restore the alcoholic function or functions which had been substituted and to obtain the desired ketonic derivatives.

Obviously the invention is not limited to the embodiments herein described and is applicable to all the biliary acids.

Having now described our invention what we claim as new and desire to secure by Letters Patent is:

1. In a method for preparing ketonic derivatives of hydroxylated biliary acids the step which consists in treating the hydroxylated biliary acid with a substance adapted to form with said acid a. water soluble compound, adding bromine to the aqueous solution of said compound, and eliminating the hydrobromic acid from the solution according as it is produced during the reaction.

2. In a. method for preparing ketonic derivatives of hydroxylated biliary acids the step which consists in treating the hydroxylated biliary acid with a substance adapted to form with said acid a water soluble compound, adding bromine to the aqueous solution of said compound and maintaining a constant value of the pH in the solution while eliminating the hydrobromic acid according as it is produced during the reaction.

3. In a method for preparing ketonic derivatives of hydroxylated biliary acids the step which consists in treating the hydroxylated biliary acid with a substance adapted to form with said acid a water soluble compound and adding to the aqueous solution of said compound bromine and a substance adapted to neutralize the hydrobromic acid produced by the reaction of said bromine with said compound.

4. In a method for preparing ketonic derivatives of hydroxylated biliary acids the step which consists in treating the hydroxylated biliary acid with a substance adapted to form with said acid a water soluble compound and adding to the aqueous solution of said compound bromine and bicarbonate of an alkali metal.

5. In a method for preparing ketonic derivatives of hydroxylated biliary acids the step which consists in treating the hydroxylated biliary acid with a substance adapted to form with said acid a water soluble compound and adding to the aqueous solution 01' said compound bromine and sodium bicarbonate.

6. In a. method according to claim 1, the further feature consisting in cooling. the aqueous solution containing said compound, said bromine and said substance during the reaction.

7. In a method according tociaim- 1, the further feature consisting in maintaining the aqueous solution containing said compound, said bromine and said substance at a temperature of about 0 C.

8. In a method for preparing ketonic derivatives of hydroxylated biliary acids containing a number 01' hydroxyl groups, the step which consists in treating the hydroxylated biliary acid with a substance adapted to form with said acid a water soluble compound, adding bromine to the aqueous solution of said compound in the amount of as many molecules of bromine for one molecule of said compound asthere are hydroxylated groups to be converted into ketonic groups, and eliminating the hydrobromic acid from the solution according as it is produced during the reaction.

9. In a method according to claim 8, the further feature consisting in adding said bromine by successive portions each formed of one'molecule oi bromine for one molecule of said compound, any one of said portions being added only when the preceding portion has been completely absorbed in the reaction solution.

10. In a. method for preparing ketonic derivatives, of hydroxylated biliary acids containing a plurality of hydroxyl groups, the step which consists, in view of changing the natural order in which the difierent hydroxyl groups are oxidized, in substituting in said hydroxylated biliary acid the hydroxyl groups, which are not to be oxidized, by other radicals not susceptible to be oxidized by the action of bromine, treating the so substituted hydroxylated biliary acid with a substance adapted to form with said substituted acid a water soluble compound, adding bromine to the aqueous solution of said compound, whereby the other hydroxyl groups will be transformed into ketonic groups in their natural order of oxidation, eliminating the hydrobromic acid from the solution according as it is produced during the reaction, and substituting, when the oxidizing is completed, said radicals not susceptible to be oxidized by hydroxyl groups.

11. In a method for preparing monoketonic derivatives of hydroxylated biliary acids containing at least one hydroxyl group, the step which consists in treating the hydroxylated biliary acid with a substance adapted to form with said acid a water soluble compound, adding bromine to the aqueous solutionof said compound in the amount of one molecule of bromine for one molecule of said compound, and eliminating the hydrobromic acid from the solution according as it is produced during the reaction. 12. In a method for preparing diketonic derivatives of hydroxylated biliary acids containing at least two hydroxyl groups, the step which consists in treating the hydroxylated biliary acid with a substance adapted to form with said acid a water soluble compound, and adding bromine to the aqueous solution of said compound in the amount oftwo molecules of bromine for one molecule of said compound, and eliminating the hydrobromic acid from the solution according as it is produced during the reaction.

13. In a method for preparing triketonic derivatives of hydroxylated biliary acids containing three hydroxyl groups, the step which consists in treating the hydroxylated biliary acid with a substance adapted to form with said acid a water soluble compound, adding bromine to the aqueous solution of said compound in the amount or three molecules of bromine for one molecule of said compound, and eliminating the hydrobromic acid from the solution according as it is produced during the reaction.

14. In a method for preparing ketonic derivatives of the cholic acid the stepwhich consists in treating the cholic acid with a substance adapted to form with said acid a water soluble compound, adding bromine to the aqueous solution of said compound in the amount of as many molecules of bromine for one molecule of said compound as there are hydroxylated groups to be converted into ketonic groups, and eliminating the hydrobromic acid from the solution according as it is produced during the reaction.

15. In a method according to claim 14, the further feature consisting in adding said bromine by successive portions each formed of one molecule of bromine for one molecule of said compound, any one of said portions being added only when the preceding portion has been completely absorbed in the reaction.

- 18. In a method according to claim 1, the iurther feature consisting after said reaction in addln! an acid to the solution so as to precipitate a ketonic acid corresponding to said hydroxylated biliary acid.

17. As a new product of manufacture the dihydromonoketocholanic acid, the melting point of which is 171 C.

18. As a new product of manufacture the hydroxydiketocholanic acid, the melting point oi. which is 129.5 C. V

RAYMOND CHARONNAT.

ALAIN HOREAU. 

